The method of preparing the model is comparatively simple. Beginning at any point upon the map, the intersection of a heavy contour line with one of the guide lines of the celluloid “position plate” is carefully noted. Both the position and the elevation of this point are fixed by the point of the altitude gauge of the modeling frame, and the clay built up beneath it to that height. With the fingers the clay is now roughly shaped in various directions from this point, the altitude gauge is advanced by the locating carriage so as to correspond in position to the intersection of the next heavy contour line with the same guide line of the position plate, and the elevation for this point similarly adjusted upon the model. As before, the surface of the clay is roughly shaped in advance and upon the sides so as to conform to the indications of the map; and this process is repeated until the work is finished. Corrections for intermediate positions may be carried to any desired degree of refinement which the scale and the accuracy of the map permit. Models which are larger than the area of the modeling frame are prepared by making a square foot at a time by the above described process, and then moving the frame forward and adjusting in a new position by means of the sharp pins in the legs of the apparatus.
Reading References
William H. Hobbs, New Laboratory Methods for Instruction in Geography, Journal of Geography, vol. 7, 1909, pp. 97-104. Also Scot. Geogr. Mag., vol. 24, 1908, pp. 643-652. The Modeling of Physiographic Forms in the Laboratory, ibid., vol. 8, 1910, pp. 225-228.
APPENDIX D
LABORATORY MODELS FOR STUDY IN THE INTERPRETATION OF GEOLOGICAL MAPS
Fig. 489.—Models to represent outcrops of rock.
The laboratory models which have been described on page 63, and are used to represent outcrops in the study of geological maps, are shown in [Fig. 489]. The drum-shaped blocks serve to represent massive rocks which occur in irregularly shaped masses such as batholites and flows. The long, narrow strips are for intrusive rocks in the form of dikes, while the larger blocks provided with a swivel joint are used for outcrops of sedimentary rocks, and after adjustment they give the dip and strike of the exposure. The wing bolts used in their construction should be of bronze, because of the effect of iron upon the compass. For the same reason tables should not be placed near iron beams or columns. All these blocks can be made by an ordinary carpenter, and should be available in sufficient numbers to arrange problems like those of [Figs. 47], [48], and [490]. With a view to supplying suggestions for other problems of the same general nature, the three additional field maps of [Fig. 491] have been introduced.